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stk::BlitSquare Class Reference

STK band-limited square wave class. More...

#include <BlitSquare.h>

Inheritance diagram for stk::BlitSquare:
stk::Generator stk::Stk

Public Member Functions

 BlitSquare (StkFloat frequency=220.0)
 Default constructor that initializes BLIT frequency to 220 Hz.
 
 ~BlitSquare ()
 Class destructor.
 
void reset ()
 Resets the oscillator state and phase to 0.
 
void setPhase (StkFloat phase)
 Set the phase of the signal. More...
 
StkFloat getPhase () const
 Get the current phase of the signal. More...
 
void setFrequency (StkFloat frequency)
 Set the impulse train rate in terms of a frequency in Hz.
 
void setHarmonics (unsigned int nHarmonics=0)
 Set the number of harmonics generated in the signal. More...
 
StkFloat lastOut (void) const
 Return the last computed output value.
 
StkFloat tick (void)
 Compute and return one output sample.
 
StkFramestick (StkFrames &frames, unsigned int channel=0)
 Fill a channel of the StkFrames object with computed outputs. More...
 
- Public Member Functions inherited from stk::Generator
 Generator (void)
 Class constructor.
 
unsigned int channelsOut (void) const
 Return the number of output channels for the class.
 
const StkFrameslastFrame (void) const
 Return an StkFrames reference to the last output sample frame.
 
- Public Member Functions inherited from stk::Stk
void ignoreSampleRateChange (bool ignore=true)
 A function to enable/disable the automatic updating of class data when the STK sample rate changes. More...
 

Additional Inherited Members

- Static Public Member Functions inherited from stk::Stk
static StkFloat sampleRate (void)
 Static method that returns the current STK sample rate.
 
static void setSampleRate (StkFloat rate)
 Static method that sets the STK sample rate. More...
 
static std::string rawwavePath (void)
 Static method that returns the current rawwave path.
 
static void setRawwavePath (std::string path)
 Static method that sets the STK rawwave path.
 
static void swap16 (unsigned char *ptr)
 Static method that byte-swaps a 16-bit data type.
 
static void swap32 (unsigned char *ptr)
 Static method that byte-swaps a 32-bit data type.
 
static void swap64 (unsigned char *ptr)
 Static method that byte-swaps a 64-bit data type.
 
static void sleep (unsigned long milliseconds)
 Static cross-platform method to sleep for a number of milliseconds.
 
static bool inRange (StkFloat value, StkFloat min, StkFloat max)
 Static method to check whether a value is within a specified range.
 
static void handleError (const char *message, StkError::Type type)
 Static function for error reporting and handling using c-strings.
 
static void handleError (std::string message, StkError::Type type)
 Static function for error reporting and handling using c++ strings.
 
static void showWarnings (bool status)
 Toggle display of WARNING and STATUS messages.
 
static void printErrors (bool status)
 Toggle display of error messages before throwing exceptions.
 
- Static Public Attributes inherited from stk::Stk
static const StkFormat STK_SINT8
 
static const StkFormat STK_SINT16
 
static const StkFormat STK_SINT24
 
static const StkFormat STK_SINT32
 
static const StkFormat STK_FLOAT32
 
static const StkFormat STK_FLOAT64
 
- Protected Member Functions inherited from stk::Stk
 Stk (void)
 Default constructor.
 
virtual ~Stk (void)
 Class destructor.
 
virtual void sampleRateChanged (StkFloat newRate, StkFloat oldRate)
 This function should be implemented in subclasses that depend on the sample rate.
 
void addSampleRateAlert (Stk *ptr)
 Add class pointer to list for sample rate change notification.
 
void removeSampleRateAlert (Stk *ptr)
 Remove class pointer from list for sample rate change notification.
 
void handleError (StkError::Type type) const
 Internal function for error reporting that assumes message in oStream_ variable.
 

Detailed Description

STK band-limited square wave class.

This class generates a band-limited square wave signal. It is derived in part from the approach reported by Stilson and Smith in "Alias-Free Digital Synthesis of Classic Analog Waveforms", 1996. The algorithm implemented in this class uses a SincM function with an even M value to achieve a bipolar bandlimited impulse train. This signal is then integrated to achieve a square waveform. The integration process has an associated DC offset so a DC blocking filter is applied at the output.

The user can specify both the fundamental frequency of the waveform and the number of harmonics contained in the resulting signal.

If nHarmonics is 0, then the signal will contain all harmonics up to half the sample rate. Note, however, that this setting may produce aliasing in the signal when the frequency is changing (no automatic modification of the number of harmonics is performed by the setFrequency() function). Also note that the harmonics of a square wave fall at odd integer multiples of the fundamental, so aliasing will happen with a lower fundamental than with the other Blit waveforms. This class is not guaranteed to be well behaved in the presence of significant aliasing.

Based on initial code of Robin Davies, 2005. Modified algorithm code by Gary Scavone, 2005 - 2006.

Member Function Documentation

void stk::BlitSquare::setPhase ( StkFloat  phase)
inline

Set the phase of the signal.

Set the phase of the signal, in the range 0 to 1.

58 { phase_ = PI * phase; };
StkFloat stk::BlitSquare::getPhase ( ) const
inline

Get the current phase of the signal.

Get the phase of the signal, in the range [0 to 1.0).

64 { return phase_ / PI; };
void stk::BlitSquare::setHarmonics ( unsigned int  nHarmonics = 0)

Set the number of harmonics generated in the signal.

This function sets the number of harmonics contained in the resulting signal. It is equivalent to (2 * M) + 1 in the BLIT algorithm. The default value of 0 sets the algorithm for maximum harmonic content (harmonics up to half the sample rate). This parameter is not checked against the current sample rate and fundamental frequency. Thus, aliasing can result if one or more harmonics for a given fundamental frequency exceeds fs / 2. This behavior was chosen over the potentially more problematic solution of automatically modifying the M parameter, which can produce audible clicks in the signal.

StkFrames & stk::BlitSquare::tick ( StkFrames frames,
unsigned int  channel = 0 
)
inlinevirtual

Fill a channel of the StkFrames object with computed outputs.

The channel argument must be less than the number of channels in the StkFrames argument (the first channel is specified by 0). However, range checking is only performed if STK_DEBUG is defined during compilation, in which case an out-of-range value will trigger an StkError exception.

Implements stk::Generator.

152 {
153 #if defined(_STK_DEBUG_)
154  if ( channel >= frames.channels() ) {
155  oStream_ << "BlitSquare::tick(): channel and StkFrames arguments are incompatible!";
156  handleError( StkError::FUNCTION_ARGUMENT );
157  }
158 #endif
159 
160  StkFloat *samples = &frames[channel];
161  unsigned int hop = frames.channels();
162  for ( unsigned int i=0; i<frames.frames(); i++, samples += hop )
163  *samples = BlitSquare::tick();
164 
165  return frames;
166 }

The documentation for this class was generated from the following file:

The Synthesis ToolKit in C++ (STK)
©1995--2014 Perry R. Cook and Gary P. Scavone. All Rights Reserved.